Login page Aligned left, need Centered

I have simple login page for our company email and it used to be centered but now with updated browsers (IE11, Chrome) it is left aligned. I've looked through the html and alignment seems to be set to centered. Can someone take a look at the code and let me know and maybe give a brief explanation on why it changed? Thanks.

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I'm not a web dev, I'm just doing a favor for my boss at work. I'm not skilled enough to know how to modernize, that's why I'm posted on EE, that I pay $13/mo for. If I wanted a smart ass comment I would have posted on the myriad of free websites. Thanks.

I don't really care what arrangement you have with EE; I am not a party to that. If you were paying my regular rate that monthly fee would buy you about 7 minutes of my time. As for the "smart ass comment"; you did not indicate your level of skill, and a professional would have used that comment as a guide to improve, instead of whining about doing a favor for the boss.

I'm not here to kiss you on the cheek, and powder your butt. When I see trash; I point it out and the majority of the users are professional who respond by addressing the issues instead of showing disrespect to people who volunteer to help from our own free time without compensation.

Vontech615,
I'm not an apologist for COBOL. But I will tell you that he is probably one of the most knowledgable experts here on EE. He has a straight forward no kit gloves kind of approach that, ahem, takes some getting used to.

I will, however, stand with him on his assessment of your code. It is ANCIENT. I haven't seen that kind of HTML in years. This is only the beginning of your bosses problems with the site. It will continue to break in strikingly curious ways as browsers upgrade. I'm hoping that it is only the form coded in this fashion and that the rest of the site is coded with web standards for modern browsers and is responsive. In April, Google will start giving negative marks to non-responsive websites.

I would highly suggest your boss invest in a site redesign. This is only the beginning of the pain. And I'm not going to be an enabler by suggesting ways to fix that archaic code.